Small interfering RNA (siRNA) has been considered as a potent tool for modulating gene expression because of its high specificity to target proteins that are not easily accessed by conventional small molecules (Gavrilov & Saltzman (2012) Yale J. Biol. Med. 85(2):187-200), hence RNAi therapeutics have demonstrated great therapeutic potential in the treatment of many devastating diseases such as cancer (Ozpolat, et al. (2010) J. Intern. Med. 267(1):44-53; Ameyar-Zazoua, et al. (2005) Exp. Opin. Biol. Ther. 5(2):221-4). However, as a naked molecule, siRNA is small and highly charged, making it susceptible to degradation, clearance and wide biodistribution (Whitehead, et al. (2011) Mol. Ther. 19(9):1688-94; Timko, et al. (2011) Annu. Rev. Mater. Res. 41(1):1-20; Shi, et al. (2011) J. Histochem. Cytochem. 59(8):727-740). On the other hand, developing carrier systems that can protect and target it to its intended site of action has shown other production and safety challenges (Whitehead, et al. (2009) Nat. Rev. Drug Discov. 8(2):129-138; Zuhorn, et al. (2007) Eur. Biophys. J. 36(4-5):4-5). These reasons collectively have limited siRNA applications beyond preclinical studies making RNAi therapeutics an unmet medical need.
Synthetic cationic materials have demonstrated considerable potential as nonviral siRNA delivery vehicles (Zuhorn, et al. (2007) supra; Yu, et al. (2012) Biomaterials 33(25):5924-5934). Cationic materials offer several benefits, including the ability to facilitate cellular uptake through contact with the negatively charged cellular membrane, enables complex formation by compressing the negatively charged siRNA through electrostatic interactions, and can potentially assist in proton sponge-mediated endosomal escape as they become more protonated with pH drop (Akinc, et al. (2005) J. Gene Med. 7(5):657-663). Yet use of these materials (e.g., polymers and cyclodextrins) has not progressed beyond initial clinical studies (Davis (2009) Mol. Pharm. Mol. Pharmaceut. 6(3):659-668) as they pose complexity, toxicity and expense barriers (Gao, et al. (2011) Int. J. Nanomed. 6:1017-25; Schroeder, et al. (2010) J. Intern. Med. 267(1):9-21). Therefore, developing an efficient inexpensive and safe delivery system is the greatest challenge associated with moving RNAi therapeutics from the bench to the bedside.
Lipid nanoparticles in general and phospholipids in particular have been generally recognized as one of the most promising delivery systems for siRNA due to their biocompatibility and ease of large scale production as well as their recent utilization in clinical trials (Yu, et al. (2012) supra; Pecot, et al. (2011) Nat. Rev. Cancer 11(1):59-67). Phospholipids are amphiphilic molecules that display physicochemical properties of naturally occurring lipids, forming a spontaneous bilayer structure upon dispersion in water (Marrink, et al. (2001) J. Am. Chem. Soc. 123(35):8638-8639), entrapping the dispersed payload within the core of the formed structure (Semple, et al. (2010) Nat. Biotechnol. 28(2):172-6; Schroeder, et al. (2010) J. Intern. Med. 267(1):9-21).
Connective tissue growth factor (CTGF) is considered the master switch in chronic fibrotic diseases (Phanish, et al. (2010) Nephron Exp. Nephrol. 114(3):e83-92; Gressner & Gressner (2008) Liver Int. 28(8):1065-1079), and provides a unique strategy for siRNA targeted therapeutics. Following chronic organ injury, CTGF is overexpressed, as a part of the wound healing response, exerting its own profibrotic effect as well as facilitating the profibrotic effect of transforming growth factor (TGF-β1). Both work synergistically causing activation of endothelial cells into proliferative myofibroblasts, causing the accumulation of collagen and other proteins in the surrounding extracellular matrix (ECM) and affecting the organ morphology and function (Phanish, et al. (2010) supra; Hernandez-Gea & Friedman (2011) Ann. Rev. Pathol. 6:425-56). Down-regulation of CTGF expression has been shown to be an effective strategy for the reversal of endothelial cells activation and accumulation of fibrotic ECM (Luo, et al. (2008) Transplant Proc. 40(7):2365-9; George & Tsutsumi (2007) Gene Ther. 14(10):790-803). The use of siRNA nanomedicine to target CTGF has been suggested (Khaja, et al. (2012) AAPS J. 14(S2); Khaja, et al. (2013) CRS Annual Meeting Abstracts 714).